The present invention relates to a data unit sending means and a method for controlling a data unit sending means.
In the field of communications, the concept of packet exchange is well known. A data packet is a given length of data whose structure is determined by a given protocol, i.e. a set of rules governing the exchange, manipulation and interpretation of such packets. Depending on the protocol, different names are used, such as frame, packet, etc. A more generic term is protocol data unit (PDU), and the following description shall use the term data unit for simplicity.
The process of sending data via a packet exchange typically comprises a plurality of protocols, which are arranged in a hierarchy. A schematic example of such a hierarchy is shown in FIG. 6. The example of FIG. 6 shows three layers, a higher layer referred to as L3, a layer below L3 referred to as L2_ARQ, and a lowest layer L1. In fact, the terms L3, L2_ARQ and L1 refer to protocols associated with these layers. As an example, L3 can be the internet protocol IP, L2_ARQ may be the radio link protocol RLP known from GSM, and L1 can be any suitable physical layer protocol.
In accordance with the concept of layering, data units associated with a higher layer are passed to a lower layer, e.g. from L3 to L2-ARQ in example of FIG. 6, where the lower layer protocol embeds the higher layer data units.
The term “embedding” may refer to encapsulation or segmentation. In the case of encapsulation, a higher layer data unit is placed into one lower layer data unit, whereas in the case of segmentation, the higher layer data unit is segmented into smaller pieces of data, each piece being placed into a lower layer data unit.
One of the important aspects of protocol layering is that in a data communication, i.e. in a process where a given amount of data is being sent from a source to a destination, the overall path that is associated with a highest layer comprises sublinks associated with the lower layer protocols, where the endpoints of a protocol of a given layer are called peers of said protocol. This concept is well known in the art and does not need to be described further here. Reference is made e.g. to the book “TCP/IP, The Protocols” by W. R. Stevens, Edison Wesley 1996.